Influences of Non-Neutral Plasma Effects on Analytical Characteristics of the Top Instruments in Mass Spectrometry for Biological Research

摘要

Understanding of the behavior of ion ensembles inside an FT ICR cell based on the computer simulations of ion motion gives rise to new ideas on cell design. The novel recently introduced FT-ICR cell based on a Penning ion trap with specially shaped excitation and detection electrodes prevents distortion of ion cyclotron motion phases (normally caused by nonideal electric trapping fields) by averaging the trapping DC electric field during ion motion in the ICR cell. Detection times of up to 5 minutes resulting in resolving power close to 40,000,000 have been reached for reserpine at m/z 609 at a magnetic field of only 7 Tesla. The fine structure of resolved 13Cn isotopic cluster groups could be measured for molecular masses of up to 5.7 kDa (insulin) with the resolving power of 4,000,000 at 7 Tesla. Based on the resolved fine structure patterns the atomic composition can be directly determined using a new developed algorithm for fine structure processing. Mass spectra of proteins and multimers of proteins reaching masses of up to 186 kDa (enolase tetramer) could be measured with isotopic resolution. For instance, at 7 Tesla the resolving power of 800,000 was achieved for the enolase dimer (96kDa) and 500,000 for molecular masses above 100 kDa. Experimental data indicates that there is practically no limit for the resolving power of this ICR cell except for collisional damping in the ultrahigh vacuum chamber. Dynamic range limits caused by Ion cloud-cloud collision is discussed. Collision of ion clouds with each other is a significant factor determining the dynamic range of the FT-ICR MS resulting in a loss of close oscillation phases for high ion densities. In most FT-ICR experiments ions were exited to close cyclotron orbits, so the ion clouds come through each other with a frequency equal to the difference of their cyclotron frequencies. Therefore the dynamic range in FT-ICR experiments could be increased by exciting different m/z ion clouds to different cyclotron radii.